Refrigeration system using gas for defrosting



Oct. 19, 1948. '0. B. LUND 2,451,682

REFRIGERATION SYSTEM USING GAS FOR DEFROSTING File d Aug. 9,1946

z: Lx A v INVENTOR. 04E 5. [0H0 BY a ' Irma/tr Patented Oct. 19, 1948 OFFICE REFRIGERATION SYSTEM USING GAS FOR DEFROSTING Ole B. Lund, Havre, Mont. Application August 9, 1946, Serial No. 689,323

, r 1 This invention relates to an automatic defrost? ing means for evaporators in coolers and refrig erators operating at below freezing temperatures.

The principal object of the invention is to provide means for automatically defrosting the cooling coils which will not require outside heating means, such as heating elements, fans, water, etc., and yet which rapidly and efiiciently removes the accumulated ice and frost.

Another object of the invention is to provide a system in which the hot gas from the compressor will be automatically circulatedthrough the cooling coils for rapid defrosting purposes whenever the freezing action becomes ineflicient due to frosting conditions and to provide means which will automatically return the system to normal operation when the accumulated ice has been removed and reduced to-an efficient operating point.

Other objects and advantages reside in the detail construction of the invention, which is de-, signed for simplicity, economy, and efficiency. These will become more apparent from the following description. I v

In the following detailed description ofthe invention, reference is had to the accompanying scams; (or; 02-2) back pressure in the suction line decreases as the rate of heat exchange at the surfaces of the evaporator coil decreases. This variation in back pressure is utilized to control the functioning of theimproved defroster system.

The improved system employs a by-pass line 20 connected to the discharge of' the compressor I2 ,of a first solenoid valve 2|. valve 22 controls the flow from the liquid line ahead of the condensor II and extending to the intake extremity of the evaporator Ill. The flow through the by-pass line is controlled by means A second solenoid IE to the expansion valve l8.

drawing which forms a part hereof. Like.nu-

merals refer to like parts in all views of the drawing and throughout the description.

The drawing illustrates a schematic diagram of the improved automatic defrosting system applied to a conventional refrigerating plant.

In the drawing, the various elements of the usual refrigerating plantare designated by numeral as follows: evaporator pipingcoil l0, condenser ll, compressor l2, compressor motor l3, accumulator [4, receiver .15, liquid line l6, suction line H, expansion valve [8, evaporator drain pan 59, circulating fan l9, power mains 53, motor control switch 54 and control circuit mains 33 and 34. The refrigerant circuit is the usual one, that is, the refrigerant is compressed and pumped by the compressor I2 into the condenser H where it liquifies and flows to the receiver I5. From the receiver 15 the liquid refrigerant flows through the liquid line Hi to the expansion valve l8 from whence it expands into thejevaporator piping coil 10. The evaporated refrigerant is then drawn backthrough the suction line I! and accumulator M to the compressor l2.

The present invention is designed to melt the accumulated frost and ice from the coil I0 whenever there is suflicient accumulation to interfere with efficient heat exchange.

The invention makes use of the fact that the -VVhen the second solenoid valve 22 is closed and the first solenoid valve 2| is open, the refrigerant cannot flow through the liquid line l6 and .mustflow through the by-pass line 20. The gas discharge from the compressor is, of course, under relatively high temperature due to the compression, and this high temperature gas flows directly through the evaporator to raise the temperature thereof and melt the ice therefrom.

The greatest accumulation of frost and ice is, of course, adjacent, the expansion valve I 8. It will be noted that the gas discharge from the bypass line 20 has a higher temperature at this point than further along through the evaporator l0. Therefore, the greatest defrosting effect is obtained at the point of greatest ice accumulation.

In order for the system to be automatic, it is necessary that some means be provided to close the second solenoid valve 22 and open the first solenoid valve 2! when the accumulation of ,ice on the evaporator coils has accumulated to an inefficient extent. It is also necessary to reset the valves 22 and 2| in their normal operating positions when theaccumulation of ice has been reduced to the desired point. This is accomplished in the present invention by connecting a pressure tube 23 with the suction line I! and extending this tube to a first expansible pressurestat 24 which operates to cause a contact blade 35 to close a contact 25 when the back pressure in the suction line reduces to a certain predetermined point.

The blade 35 is connected to the control main 34 and the closing, of the contact 25 completes a circuit through a conductor 26 with a relay magnet 21. The circuit through the magnet 21 is completed through a conductor 28 toa contact 29 which is contacted by a contact blade 30 actuated by a thermostat 3| connected by means of a bulb tube 56 with a thermostatic bulb 51 positioned on one of the coils of the evaporator I 0.

enemas 3 The blade Si! is grounded by means of a conductor 32 to the control main 33. A first thermostat blade 68 is in circuit with the conductor 3'2. The blade 58 is actuated from a room or fixture thermostat control 58.

The relay magnet 2'! actuates an armature 36. The armature 36, when attracted, breaks two contacts 31 and 38 and closes two contacts 39 and 40. The contact 38 is connected by means of a conductor 4| with the second solenoid valve 22, from which a ground line 42 leads to the control circuit main 33. A second thermostat blade 6| is in circuit with the conductor 4|. This blade is mounted with the first blade 60 so that both act in unison under the influence of the room control 58.

The contact 39 is connected by means of a conductor 43 with a contact which is closed by a switch blade 45 actuated by a second pressurestat 46 connected by means of a pressure tube 41 with the discharge extremity of the condenser The blade 45 is connected to one side of the first solenoid valve 2| by means of a conductor 52.

The relay contact 4|) is connected to the conductor 26 leading to the magnet 21. v The relay contact 31 is connected by means of a conductor 48 with the circulating fan IS. The relay armature 35 is connected to the circuit control main 34 by means of a conductor 49. The fan I9 is grounded to the control main 33 by means of a ground lead 50, and the first solenoid valve 2| is similarly grounded by means of-a ground .line|.

a switch member 63 to close a-contact 64 upon reduction of pressure. in the suction line H. The

pressurestat 55 is set to break its contact at alower back pressure than will act to break the ing the first solenoid valve 2| to open the latter.

The hot gas from the compressor |2 now flows through the by-pass line into the evaporator to rapidly raise the temperature thereof and melt the ice and frost therefrom.

The temperature of the evaporator coils rises and. when this temperature. reaches a certain predetermined point, the thermostat 3| will expand to open the contact 29, breaking the circuit to the relay magnet 21, allowing the armature 36 to return to normal position. This immediately places the system back in its normal operating condition under the control of the thermostat control 58.

Some means must be provided for maintainin the circuit to the relay magnet 2? closed after the hot gas begins to flow into the evaporator, since the increased gas pressure would immediately expand the first pressurestat 24 to open the contact 25. This is accomplished by connecting the relay contact 40 to the conductor 26 so that thelatter contact will hold the circuit to the relay magnet closed after the contact is open.

During the operation of the defrosting system the pressure in the condenser naturally falls.

v To prevent the pressure in the condenser from dropping to a point where it might freeze the condenser; the second pressurestat 46 is employed. The drop in pressure 'in the condenser isimmediately communicatedto the pressurestat 4B, and when this pressure reachesa low point of, say 50 p s. i., the switch blade 45j'will open'the contact 44.:closing the second solenoid I valve'2l and forcing the hot gas toflow through the condenser until the pressure therein has raised to a; bra-set point of, say 135 p; at which timethei second pressurestatfifi will cause the switch bladejfito con'tact the contact 44 and circuit at the first pressurestat 24. The switch member 63 and the contact arein. series with apilot circuit carrying current fromthe' c trol mains 33 and 34 to the actuating mechanism of the motor switch control 54.

As illustrated the control circuitmainsarenar 34 are being supplied with current from the power mains 53 through a suitable transformer 66. The

type of current and the sources of supply depend upon the sources available at the point of installation and form no part of the present invention.

In the drawing, the various contacts are illustrated in the normal running position. The circuit to the relay magnet 21 is open at the contact 25, The circuit to the fan l9 and the second solenoid valve 22 are closed by means of the relay armature 3G. The circuit to the compressor ."notor I3 is closed at the switch control 54 through he influence of the closed pilot circuit 65. The fan and the compressor are operating and the system is functioning in the usual manner.

Operation in the room -or.;fiXtur-e v g the-circuitsicontrolled .therebyjjare opened In thedmpr'oved defrost ng System this thermostat 5fsimul neously opens two circuits; one through theeonductor 32 "and one through the conductor again .close the circuit Zto openfthe .valve 2l Th roomzjthermosta control .SS'fiInpti ns in the usual mannerym below a presetfipoint 4|, whenthe proper'room temperature is reached.

When thecir cui't through the conductor 4| is opened, the second solenoid valve 22 closes allowing the pressure in the suctionline I! to reduce sufficiently to actuate the low pressurestat 55 to break contact at 63-54 stopping the compressor and the system. This also actuates the first pressurestat 24 but since the circuit through the conductor 32 is open at the thermostat control 58 the current supply to the defrost ng relay magnet 21 is cut off during idle periods of the condensing unit.

Ice loosened by the defroster may fall to the drain pan 59. In order to prevent this ice from freezing to the pan, the by-pass line 20 is conducted beneath the pan in contact therewith, as indicated at 68, so that the temperature of the pan 59 will be raised when the temperature of the evaporator is raised so as to melt the ice in the pan.

The relay and the various pressurestats and thermostats may be mounted on a control board located at a suitable point and indicated in broken line at 61. The motor control switch 54 and the room thermostat control 58 may be mounted in the customary manner.

Having thus described the invention, what is claimed and desired secured by Letters Patent is:

1. In a refrigerating system having a gas comwho; the temperature pressor, a suction line leading from said evaporator to said compressor, a condenser receiving the gas from the compressor, and a liquidline carrying the liquid gas from the condenser to the evaporator, means for defrosting the evaporator comprising: a by-pass line extending from the discharge of the compressor to the intake of the evaporator; an electrically controlled valve in said by-pass line; a second electrically controlled valve in said liquid line; a pressure-operated switch connected to the suction line; electric contacts controlled by said switch, said contacts being arranged to open the first valve and close the second valve when the pressure in the suction line has decreased to a pre-determined point; and means for closing the first valve when the pressure in the condenser has decreased to a certain pre-determined point.

2. In a refrigerating system having a gas compressor, a suction line leading from said evaporator to said compressor, a condenser receiving the gas from the compressor, and a liquid line carrying the liquid gas from the condenser to the evaporator, means for defrosting the evaporator comprising: a by-pass line extending from the discharge of the compressor to the intake of the evaporator; an electrically controlled valve in said by-pass line; a second electrically controlled valve in said liquid line; a pressure-operated switch connected to the suction line; electric contacts controlled by said switch, said contacts being arranged to open the first valve and close the second valve when the pressure in the suction line has decreased to a, pre-determined point; a second pressure-operated switch; and means for conducting pressure to said second switch from the condenser, said second switch being in circuit 6 with said first valve to close the latter when the pressure in the condenser has lowered to a predetermined point.

3. In a refrigerating system having a gas compressor, a suction line leading from said evaporator to said compressor, a condenser receiving the gas from the compressor, and a liquid line carrying the liquid gas from the condenser to the evaporator, means for defrosting the evaporator comprising: a by-pass line extending from the discharge of the compressor to the intake of the evaporator; an electrically controlled valve in said by-pass line; a second electrically controlled valve in said liquid line; a pressure-operated switch connected to the suction line; a relay controlled by said switch; means for conducting pressure from the suction line to operate said switch when the pressure in the suction line decreases to a pre-determined point; a first contact closed by the operation of said relay said first contact being in circuit with said first valve; and a second contact broken by the operation of said relay, said second contact being in circuit with said second valve; and means for opening the circuit controlling said relay when the temperature of the evaporator rises to a pre-determined point.

OLE B. LUND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,114,766 Heitman Apr. 19, 1938 2,351,140 McCloy June 13, 1944 2,433,574 Newton Dec. 30, 1947 

